Biowaste Valorization to Produce Advance Carbon Material-Hydrochar for Potential Application of Cr (VI) and Cd (II) Adsorption in Wastewater: A Review

Abstract

The dramatic increase in the use of biomass waste has caused a serious environmental pollution phenomenon. Biowaste valorization to produce advanced material-hydrochar is regarded as a promising carbon neutrality technology for biomass waste recycling and utilization. Hydrochar obtained by hydrothermal carbonization has attracted much attention due to its regular morphology, good physical and chemical stability, and abundant oxygen-containing functional groups on the surface. This reviews the preparation of hydrochar and the basic methods of modified hydrochar and expounds on the related reaction mechanism of adsorption. The adsorption and recovery of heavy metals, Cr (VI) and Cd (II), in wastewater by hydrochar were focused on. The experimental conditions of hydrochar, such as synthesis temperature, synthesis time, modified condition, adsorption capacity, adsorption isotherm, and adsorption kinetics, were compared. The adsorption conditions of hydrochar for Cr (VI) and Cd (II) in wastewater, including the adsorption pH value, the adsorption time, the adsorption temperature, and so on, have been summarized. The review develops a better understanding of Cr (VI) and Cd (II) adsorption by hydrochar in wastewater, making an innovative perspective for the improvement and large-scale application of hydrochar as an advanced carbon material as well as biowaste utilization.